///////////////////////////////////////////////////////////////
//  Copyright 2012 John Maddock. Distributed under the Boost
//  Software License, Version 1.0. (See accompanying file
//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_

#ifndef BOOST_MP_INTEGER_HPP
#define BOOST_MP_INTEGER_HPP

#include <boost/multiprecision/cpp_int.hpp>

namespace boost{
namespace multiprecision{

template <class Integer, class I2>
typename enable_if_c<is_integral<Integer>::value && is_integral<I2>::value, Integer>::type
   multiply(Integer& result, const I2& a, const I2& b)
{
   return result = static_cast<Integer>(a) * static_cast<Integer>(b);
}
template <class Integer, class I2>
typename enable_if_c<is_integral<Integer>::value && is_integral<I2>::value, Integer>::type
   add(Integer& result, const I2& a, const I2& b)
{
   return result = static_cast<Integer>(a) + static_cast<Integer>(b);
}
template <class Integer, class I2>
typename enable_if_c<is_integral<Integer>::value && is_integral<I2>::value, Integer>::type
   subtract(Integer& result, const I2& a, const I2& b)
{
   return result = static_cast<Integer>(a) - static_cast<Integer>(b);
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value>::type divide_qr(const Integer& x, const Integer& y, Integer& q, Integer& r)
{
   q = x / y;
   r = x % y;
}

template <class I1, class I2>
typename enable_if_c<is_integral<I1>::value && is_integral<I2>::value, I2>::type integer_modulus(const I1& x, I2 val)
{
   return static_cast<I2>(x % val);
}

namespace detail{
//
// Figure out the kind of integer that has twice as many bits as some builtin
// integer type I.  Use a native type if we can (including types which may not
// be recognised by boost::int_t because they're larger than long long),
// otherwise synthesize a cpp_int to do the job.
//
template <class I>
struct double_integer
{
   static const unsigned int_t_digits =
      2 * sizeof(I) <= sizeof(long long) ? std::numeric_limits<I>::digits * 2 : 1;

   typedef typename mpl::if_c<
      2 * sizeof(I) <= sizeof(long long),
      typename mpl::if_c<
         is_signed<I>::value,
         typename boost::int_t<int_t_digits>::least,
         typename boost::uint_t<int_t_digits>::least
      >::type,
      typename mpl::if_c<
         2 * sizeof(I) <= sizeof(double_limb_type),
         typename mpl::if_c<
            is_signed<I>::value,
            signed_double_limb_type,
            double_limb_type
         >::type,
         number<cpp_int_backend<sizeof(I)*CHAR_BIT*2, sizeof(I)*CHAR_BIT*2, (is_signed<I>::value ? signed_magnitude : unsigned_magnitude), unchecked, void> >
      >::type
   >::type type;
};

}

template <class I1, class I2, class I3>
typename enable_if_c<is_integral<I1>::value && is_integral<I2>::value && is_integral<I3>::value, I1>::type
   powm(const I1& a, I2 b, I3 c)
{
   typedef typename detail::double_integer<I1>::type double_type;

   I1 x(1), y(a);
   double_type result;

   while(b > 0)
   {
      if(b & 1)
      {
         multiply(result, x, y);
         x = integer_modulus(result, c);
      }
      multiply(result, y, y);
      y = integer_modulus(result, c);
      b >>= 1;
   }
   return x % c;
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value, unsigned>::type lsb(const Integer& val)
{
   if(val <= 0)
   {
      if(val == 0)
      {
         BOOST_THROW_EXCEPTION(std::range_error("No bits were set in the operand."));
      }
      else
      {
         BOOST_THROW_EXCEPTION(std::range_error("Testing individual bits in negative values is not supported - results are undefined."));
      }
   }
   unsigned index = 0;
   Integer mask = 1;

   while(((mask & val) == 0) && (index < sizeof(Integer) * CHAR_BIT))
   {
      ++index;
      mask <<= 1;
   }
   return index;
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value, bool>::type bit_test(const Integer& val, unsigned index)
{
   Integer mask = 1;
   if(index >= sizeof(Integer) * CHAR_BIT)
      return 0;
   if(index)
      mask <<= index;
   return val & mask ? true : false;
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value, Integer&>::type bit_set(Integer& val, unsigned index)
{
   Integer mask = 1;
   if(index >= sizeof(Integer) * CHAR_BIT)
      return val;
   if(index)
      mask <<= index;
   val |= mask;
   return val;
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value, Integer&>::type bit_unset(Integer& val, unsigned index)
{
   Integer mask = 1;
   if(index >= sizeof(Integer) * CHAR_BIT)
      return val;
   if(index)
      mask <<= index;
   val &= ~mask;
   return val;
}

template <class Integer>
typename enable_if_c<is_integral<Integer>::value, Integer&>::type bit_flip(Integer& val, unsigned index)
{
   Integer mask = 1;
   if(index >= sizeof(Integer) * CHAR_BIT)
      return val;
   if(index)
      mask <<= index;
   val ^= mask;
   return val;
}

}} // namespaces

#endif
